1. Field of the Invention
The present invention relates to improvements of a magnetic recording medium used for magnetic recording and/or reproducing apparatus such as a video tape recorder and a digital audio tape recorder, and it particularly relates to a coated-type magnetic recording medium having a non-magnetic film base on which a magnetic layer containing resin is provided.
2. Description of the Related Art
Presently, in a magnetic tape used for a video tape recorder as a magnetic recording medium, a thickness of the magnetic tape is required to be as thin as possible to meet a demand for the magnetic tape capable of long play.
On the other hand, reducing the thickness of the magnetic tape substantially degrades a mechanical strength of the magnetic tape, which also tends to cause degradations of electro-magnetic conversion characteristics because of a degradation of a head-tape contact characteristic between a magnetic head and the magnetic layer and to cause tape damages such as folds and creases by contacting with tape guide members for restricting running of the magnetic tape.
Further, reducing the thickness of the magnetic tape causes a deformation of a recorded pattern (referred to as a degradation of a track linearity, which is required to be less than or equal to 10 .mu.m ), which poses degradations of electro-magnetic conversion characteristics and a degradation of an interchangeability of a recorded tape among different tape decks.
As a countermeasure to these problems, it is tried to increase a strength of a polyester film employed as a non-magnetic film base (referred to as a film base) for supporting the magnetic layer thereon and to increase a mechanical strength of the magnetic tape by forming the magnetic layer having a high elastic modulus on the film base, however, this countermeasure does not meet the demand enough.
As measures for improving the strength of magnetic tape, it is proposed in Japanese Laid Open Patent Publication 56-11624/1981 and 62-62424/1987 that aramid resin is employed as the film base instead of the polyester resin. Further, it is proposed in Japanese Laid Open Patent Publication 63-298810/1988 that a Young's modulus Y(TD) in a traversing direction of the magnetic tape is made larger than a Young's modulus Y(MD) in a longitudinal direction of the magnetic tape, and in Japanese Laid Open Patent Publication 4-44628/1992 that the Young's modulusli Y(TD) and Y(MD) in the traversing and longitudinal directions of the magnetic tape are respectively determined to be approximately 800 Kg/mm.sup.2.
However, when the aramid resin film is employed as the film base of the magnetic tape, it is difficult for a mass-production of magnetic tapes because of a low productivity, as that which increases the manufacturing high cost of the magnetic tape.
Further, even though the Young's modulus Y(TD) in the traversing direction of the magnetic tape is made larger than the Young's modulus Y(MD) in the longitudinal direction, there are problems that the electro-magnetic conversion characteristics of the magnetic tape are degraded due to the degradation of a head-tape contact characteristic if the overall thickness of the magnetic tape is made less than 12.5 .mu.m. Further, even though the Young's modulusli Y(TD) and Y(MD) in the traversing and longitudinal directions of the magnetic tape are respectively determined to be approximately 800 Kg/mm.sup.2, there are problems that both the mechanical strength and the electro-magnetic conversion characteristic of the magnetic tape are degraded if the overall thickness of the magnetic tape is made less than 12.5 .mu.m.